Sudan, once the largest and one of the most geographically diverse states in Africa, split into two countries in July 2011 after the people of the south voted for independence.

The government of Sudan gave its blessing for an independent South Sudan, where the mainly Christian and Animist people had for decades been struggling against rule by the Arab Muslim north.

However, various outstanding issues - especially the question of shared oil revenues and border demarcation - have continued to create tensions between the two successor states.

Sudan has long been beset by conflict. Two rounds of north-south civil war cost the lives of 1.5 million people, and a continuing conflict in the western region of Darfur has driven two million people from their homes and killed more than 200,000.